This invention relates to magnetic disk file systems of the type used primarily in connection with computer systems as memory storage. More particularly this invention relates to the fine positioning control system for the magnetic heads in such magnetic disk files. A head control system is provided in which a fine position feedback control signal is derived solely from a head position error signal.
An earlier effort at providing a position responsive servo feedback loop in a magnetic disk file is illustrated by U.S. Pat. No. 3,246,307. This patent relates to a disk system having comparitively low track density compared to present day, state of the art, systems. Consequently, the patent implies that when the position error signal is at a zero value, the fine tracking characteristics of the head with respect to the magnetic disk track is fully corrected. This is not the case, however, since even a position error signal having a zero value, based on its history, can have a velocity component which requires a position correction component. This further correction component is required in high track density disks representative of the present state of the art.
Typically, the manner in which the present state of the art high track density, magnetic disk files obtain velocity information for head position correction purposes is by use of a velocity transducer such as a stationary coil in proximity to a magnet mounted on the head arm assembly or by measuring current changes in the voice coil actuator for the head arm assemblies. Thus, typical present state of the art system would have two separate signals generated in order to control head positioning.
One problem with a second source of head information is that it is typically obtained from a location remote from the head. Where this information is obtained from a remote transducer, such as a velocity transducer associated with the rod that passes through the voice coil, extraneous signals are introduced partially because of mechanical couplings and linkages. Where the requirement is to position the head and obtain information about head position, it is desirable to get the information directly from the head.